1. Field of the Invention
The present invention relates to a semiconductor device having a circuit composed of thin film transistors (hereinafter, referred to as TFTs) and a method of manufacturing the semiconductor device. For example, the present invention relates to an electro-optical device typified by a liquid crystal display panel and an electronic equipment mounted with the electro-optical device as a component.
Note that the term semiconductor device in this specification indicates devices in general capable of functioning with the use of semiconductor characteristics, and electro-optical devices, semiconductor circuits and electronic equipment are all included in the category of the semiconductor device.
2. Description of the Related Art
In recent years, a technology of constituting a thin film transistor (TFT) by using a semiconductor thin film (with a thickness of approximately several to several hundred of nm) formed on a substrate having an insulating surface has attracted attention. The thin film transistor is widely applied to an electronic device such as an IC or an electro-optical device, and needs to be developed promptly as, in particular, a switching element of an image display device.
An active matrix liquid crystal module is known as a typical example of the thin film transistors. Particularly, a TFT having a silicon film having a crystalline structure (typically, polysilicon film) as an active layer (hereafter, referred to as polysilicon TFT) has high filed-effect mobility compare to a TFT having a silicon film having a amorphous structure (typically, amorphous silicon film), and thus such TFTs are multiused recently.
Although there are various technologies of obtaining the silicon film having crystalline structure, especially, a technology given in Japanese Unexamined Patent Publication No. Hei. 8-78329 official report, in which the metallic elements (typically nickel) promoting crystallization to an amorphous silicon film are added alternatively, thereby performing a heat treatment to form the crystalline silicon film which spreads with an addition region as the starting point. Since the size of the crystal grain obtained thereof is very large compared with other technologies, and the field effect mobility is high, various circuits equipped with various functions can be formed thereby. For example, in case of using the technology of the above-mentioned official report, to a liquid crystal module carried in a liquid crystal display device, drive circuits for controlling pixel portions, such as pixel portions which perform an image display for every functional block, a shift register circuit based on a CMOS circuit, a level shifter circuit, a buffer circuit, and a sampling circuit, and the like can form on one substrate.
Moreover, the above-mentioned official report technology can lower approximately 50–100° C. crystallization temperature of an amorphous silicon film by the action of metallic elements compared to a method without using metallic elements, thereby a glass substrate can be used without any problems occurring in process. Moreover, required time in the crystallization of the above-mentioned official report technology can be reduced to ⅕– 1/10 compared to the method without using metallic elements, thereby the above-mentioned official report technology is also excellent in productivity.